Loading...
HomeMy WebLinkAboutGreen Seal's Choose Green Report - Low Rolling Resistance Tires '.. eE~ r . ._ ll- MARCH 2003 ~ LOW ROLLING RESISTANCE TIRES a - 80% or more of a car's fuel energy is wasted by friction and W other such losses ~ - 1.5 to 4.5% of total gasoline use could be saved if all replacement tires in use had low rolling resistance - About 237 million replacement tires are sold in the U.S. each year -none has rolling resistance labeling - This report presents previously unpublished data on leading tires with low rolling resistance America's Fuel Use, Its Impacts, and Opportunities for Savings he environmental impacts of America's gasoline use are profound. With over 160 million passenger cars and light trucks on the road, we burn about 126 billion gallons of gasoline per year. Our fuel use continues to rise about 3% annu- ally, propelled by continued increases in total number of vehicles, rising average distance driven per car, and falling average fuel economy. Today, light-duty vehicles (cars & light trucks) are responsible for about 20% of the nitrogen oxides, 27% of the volatile organic com- pounds, 51% of the carbon monox- ide, and roughly 30% of all the carbon dioxide (the main green- house gas) emitted from human activities nationwide. Rising fuel use also has enormous implica- tions for protection of wilderness and public lands (vulnerable to increased exploration), water resources (vulnerable to tanker and pipeline accidents), and national security. So the opportu- nity to save money and improve environmental quality through fuel use reductions is clear. One of the most promising opportunities for fuel savings across the entire fleet of existing vehicles is to utilize low rolling resistance tires instead of stan- dard replacement models. This change improves the inherent efficiency of the vehicle, automati- cally saving fuel over the typical 30,000 to 50,000 mile lifetime of a set of tires. This report examines the opportunity for saving gasoline through use of improved fire technology and recommends particular fire models for which our initial test data suggest environ- mental advantages. Its findings are applicable to government and corporate fleet managers as well as individual fire buyers. How Tires Can Reduce Fuel Consumption According to the National Acad- emy of Sciences, about 80 to 88% of the energy in a vehicle's gaso- line tank is wasted in various thermal, frictional, and standby losses in the engine and exhaust system. This leaves only about 12 to 20% of the potential energy actually converted to vehicle motion. One of the key ways to improve that efficiency is to reduce the rolling resistance of vehicle tires. This is not a measure of a tire's traction or "grip" on the road surface, but rather simply indi- cates how easily a fire rolls down the road, minimizing the energy wasted as heat between the fire and the road, within the fire sidewall itself, and between the fire and the rim. Detailed modeling conducted by the National Renewable Energy Laboratory concluded that a 10% reduction in fire rolling resistance should yield fuel savings of about 1 to Z%, depending on driving conditions and vehicle type. According to research for the California Energy Commission, about 1.5 to 4.5% of total gasoline use could be saved if all replace- ment tires in use had low rolling The Choose Green Report is published for Green Seal Environmental Partners. To become an Environmental Partner, or to receive a copy of this report, contact Green Seal at 202-872-6900 or grcenseal@ greenseal.org. Green Seal President and CEO, Arthur 6. Weissman Researchers, My Ton, Chris Colwell, and Trauis Reeder, Ecos Consulting Design, Cutting Edge Design Support provided by the Energy Foundation Printed on Green Seal-certified Mohawk Satin Cool While Recycled paper, 30% postconsumer content Copyright ®2003, Green Seal, Inc. www.grccaseal.org GREEN SEAL EnriroeMrntal Parfaer 2 Choose Green Report resistance. This translates roughly into average savings of up to 30 gallons of gasoline savings per vehicle per year, or from $2.5 to $7.5 billion worth of national average gasoline savings. As part of their efforts to meet Federal fuel economy standards, automakers routinely specify low rolling resistance tires on their new vehicles. Between 1980 and 1994, the lowest rolling resistance fire models available achieved a 48% reduc- tion in rolling resistance, As part of their and have e,~°orts to meet likely contin- ued to Federal fuel improve economy thereafter. standards, These original equipment automakers (OE) tine routinely models are specify low occasionally available in rolling the replace- resistance tires ment tine on their new market, but often only by vehicles. special order. In general, the tires marketed to the replace- ment fire market tend to place greater emphasis on longevity and low price, and therefore often have higher rolling resistance than OE tires. Unfortunately both OE and replacement tires lack any sort of rolling resistance labeling cur- rently, so fleet managers and consumers that wish to buy highly energy-efficient tires when their first set of OE tires wear out have been stymied. Even when tine makers claim that particular replacement models are more fuel- efficient than others, they do not always use consistent test methods or independent laboratory data to back up those claims. About 237 million replacement tires are sold in the U.S. each year for cars and light trucks, and none of them provides rolling resistance labeling. In 2002, the Energy Foundation funded Ecos Consulting to analyze the fire market, select representa- tive models for rolling resistance testing, and work with Green Seal to recommend particular models that perform well while achieving low rolling resistance. Those findings are being published for the first time in this Choose Green Report. Additional background on Ecos Consulting's key findings can be found in a separate report prepared for the California Energy Commission, available at www.energy. ca.gov/reports/2003- Ol -31 600-0 3-001 CRVOL2. PDF. Balancing Tire Resistance and Other Considerations The manufacture of tires, like other industrial processes, involves material extraction and produc- tion, as well as energy consump- tion and the emission of various pollutants. Each of these manufac- turing stages impacts the environ- ment indifferent ways. However, tires, like a number of other consumer products, are actually responsible for more environmen- tal impacts in their use and ultimate disposition than in their manufacturing. They significantly impact the amount of fuel con- sumed by the vehicle to which they are attached, leading to global warming emissions as well as local and regional air pollution. They create particulate air pollution in the process of wearing, and they can be a significant solid waste problem if not properly recycled. An analysis conducted by Italian fire manufacturer Pirelli (Figure 1) revealed the dominance of fire use in overall life-cycle energy con- sumption. Fully 82% of the life- cycle energy use occurs from the tire's contribution to vehicle fuel use, compared to roughly 18% associated with obtaining the raw materials and manufacturing the Collection m Endof-Life O.OS6% ~ Raw Marorials 14.097% Use (Tire D$Z% and Fuel) Compound Recycling o.19a% Tire Production s.9so^i Disfribufion 0.076% Source: Pirelli SA ~~.:" 'r ~' fire itself. Thus, a tire's rolling resistance is likely to be a larger factor in its life-cycle environmen- tal impact than its composition, longevity, or ultimate fate, though those factors merit consideration as well. This report places greatest significance on the measured rolling resistance of tires, followed closely by consideration of the tire's expected longevity and performance characteristics. Afire with high rolling resistance can cause pro- found environmental impact, even if it capably grips the road and lasts for 80,000 miles. By contrast, a very low rolling resistance fire may not be worth recommending if its lifetime is unusually short or test data indicate that it provides poor traction. Every fire currently on the market represents a balance between a wide assortment of desired performance characteris- tics and price (we surveyed tires ranging from $25 to over $200 per tire). Careful balancing of these characteristics can yield not only a high-performing tire, but also one that is better for the environment than others currently available on the market. Rating Tire Rolling Resistance and Related Factors Rolling resistance has traditionally been measured through an official Society of Automotive Engineers (SAE) test procedure known as J1269. It measures the force required to roll a fire against a dynamometer at a fixed speed of 50 miles per hour. A newer procedure, SAE J2452, promises improved accuracy by assessing rolling resistance at a variety of speeds, but no independent laboratory currently has the capability to conduct such testing in-house. As a result, all of our testing was conducted at a single independent laboratory according to SAE Ji269. The highest and lowest rolling resistance tires we tested differed in efficiency by 60%, indicating that fire choice can have a bigger impact on fuel economy than most people realize. Rolling resistance differences of 20 to 30% are not uncommon among tires of an otherwise similar size, type, and level of performance. This means an individual vehicle could save up to 6% of its gasoline use if it were fitted with very efficient tires, paying for the modest additional cost of low rolling resistance tires in approximately a year of fuel savings. In other words, a typical compact car such as a Ford Focus can improve its mileage from 30 mpg to 32 mpg simply by using lower rolling resistance tires. For a car averaging 15,000 miles per year the fuel savings is about $50 (at $1.50 per gallon) All tires have imprinted infor- mation on their sidewalk indicat- ing size, type, load, and speed ratings, as described in Figure 2. The majority of fire models employ a "P" designation for passenger vehicle use, but some bear the "LT" designation for use with light trucks. In general, "P" tires appear to be gaining in popularity relative to "LT" tires of a given size. In addition, the U.S. Department of Transportation requires each manufacturer to grade its tires under the Uniform Tire Quality Grading System (UTQGS) and establish ratings for the following characteristics: tread wear, trac- tion, and temperature resistance. Unfortunately, the ultimate results published for each fire model are less "uniform" than they should be. The government specifies how each test should be conducted and prevents a manufacturer from claiming better performance than measured. However, it does not prevent manufacturers from claiming worse performance than measured. And, curiously enough, many do, primarily to amplify marketing distinctions among their tires at difi'erent price points and encourage buyers to move up from a "good" to a "better" or "best" model in a particular category. Given the variability of ratings and the number of relevant factors, we have compiled our own composite metrics of performance for assessing tires, including the Federal ratings noted below and a variety of other published data, as follows: Choose Green Report 3 a minimum traction rating of "A." Traction in a wide variety of other circumstances (cornering, dry conditions, snow, etc.) can also be very important, so we evaluated test data from Con- sumer Reports where available, which included considerations of the impact of antilock braking systems as well. We also evalu- ated Tire Rack.com customer survey data on traction in a variety of road conditions, averaging the data available for each model to produce a composite traction score. rt. zos - wsdth of ase srs ~. 55 • aspect ratb sthka sidewax~s haipht ii rau4i-tY ! of qta ~s widdU. 3. R • ~ I tsufskruttian. 6, 16.Oiarrfatef Ot th8 whldt fin iEK11@5~ on which the ttre ilts_ s. nst - aumerk~ roue assocsaced mss maaiinrurn sued a are can c3rsy. ^ ROLLING RESISTANCE - We assessed rolling resistance for 51 different currently available fire models in four sizes. These models represent only a fraction of the hundreds of models currently available today, but were chosen because previous tests or manufacturing claims indicated they might have lower than average rolling resistance or other distinctive performance features (best wet traction, high overall satisfaction, etc.). The models we tested had rolling resistance coefficients ranging from 0.0062 to 0.0152 (see Figure 3). We recommend models with an RRC of 0.0105 or less, recognizing that low values are somewhat more difl"icult to achieve on larger, heavier tires than on smaller, lighter weight models. ^ TREAD WEAR -The UTQGS test assesses how much tread is lost from a particular fire after being driven a known distance on a government test course. A fire with a score of 200 would have half the wear (and roughly 4 Choose Green Report a v - spsen ratsnR s+~ss esra aaaa unWe apeaut sps to ~ rtopsp. !. XGT y - Man~er'i tsarrw far sxeas sres~lueturst. 5aasra tlesigea~tbns may Ise pr+eoeded' by a'P." stssrarvllntN Pa45atN~[ Source: www.tireadvisor.com twice the longevity) of a fire that scored 100. Few tires score less than 100, while the most durable models are rated at 600, 700, or more. Scores of 350 or more indicate above- average levels of durability, and we recommend a minimum rating of 300. We also evaluated two other measures of fire durability from several Internet sources (including Tire Rack.com), where available: our information represents cus- tomer survey responses reflect- ing over Z billion miles of total driving, and assessments of manufacturer warranties that consider both the total mileage covered and the comprehen- siveness of the warranties. We averaged all the data available for each model to produce a composite tread wear score. ^ TRACTION -The UTQGS mea- sores straight-line fire wet braking traction and reports fire performance using qualitative grades of AA, A, B, or C, with AA being the highest. We recom- mend that you choose tires with ^ OVERALL CUSTOMER SATISFACTION -Tire Rack.com has asked its customers if they would buy various fire models again. The response received, on a scale of 1 to 10, reflects the best overall indicator of cus- tomer satisfaction with particu- lar fire models, reflecting traction, handling, value, noise, and comfort. Note: We did not employ the UTQGS temperature resistance values (A, B, or C) when selecting tires for this report. While "A" rated tires are generally preferred, the link- ages between high temperature resistance and greater longevity or lower rolling resistance are still somewhat controversial. 'IYead wear, traction, and customer satisfaction scores were averaged into an overall composite performance score. The average score for the 450 fire models in our database was 6.82. Such results are still imperfect, in part because Consumer Reports test data and TireRack.com data are not avail- able for all models, leading to excessive reliance on the flawed UTQGS values for some tires. Green Seal's fire recommendations represent tires with a greater than average performance score and a ~ ~,~ ~ twiaewar~ rolling resistance coefficient of less than 0.0105. These are listed individually in Table 1. Note that the tire sizes listed are the individual sizes that we tested, but most models are available in a wide array of sizes. Because of the difference in tire weights across the various sizes, absolute RRCs are more meaningful within a particular size than across a • ~ • • ~ • ~ • ~ 0 016 . 0 185/7414 Not Recommended • 185/70.14 Recommended ~ ^ c 0 205/55-Ib • 205/55-16 A~eroge Performance Score for All Tires in m 0.014 ^ 235/75-15 ^ 235/75-15 Database' 6.82 ~ °^ ° 245/75-16 • 245/75-16 j ~ o.olz o ~ ° o m r fr~ ^ O ~ O 00 O .-_- ai- - ' _. ~ _ 9 __ - ri o.olo O ~ ~~ ~ I o ^ o o °~ • • m ° O ~• c 0.008 ^ ^ ~ ^ 0 0.006 • 0.004 3 4 5 6 7 8 9 Performance Composite Score range of sizes. However, a tire model that managed a relatively low rolling resistance within one size is likely to perform relatively well in a different size as well, all other things being equal. Also note that some of the recommended models are all season radials or performance-oriented models, while others are snow tires. Be sure to choose the model that best suits your needs (websites like tireadvisor.com and tirerack.com can assist with that process). Rolling On to the Future Efforts to differentiate replace- ment tires on the basis of rolling resistance are still in their very early stages. Without data on the rolling resistance of all tine models across a range of sizes, it is impossible to say for sure if the models identified in this report represent the most efficient models or simply a subset of them. For now, consumers and fleet manag- ers can start with the data shown here and request additional information directly from retailers and manufacturers. ` Low-rolling-resistance tires ~~JU~~~~:~Q~tfiJ ~, Low-rolling-resistance tires In the endless quest for better fuel economy, it's easy to overlook the role that tires can play. However, a tire's inflation pressure, weight, and rubber chemistry all contribute to how much fuel it takes to push that tire down the highway. While inflation pressure is something you can (and should) check regularly, important factors that might influence your choice of tires, such as rolling resistance, are invisible to a consumer. Automakers often specify low-rolling-resistance tires as original equipment to enhance vehicle performance in government fuel-economy tests. However, when it comes time to replace the factory-fitted tires, it is important to consider the full spectrum of tire performance. After all, replacement tires are not limited to any vehicle manufacturer's requirements. Replacement tires generally have well- rounded all-season grip and longer tread life, as opposed to optimal rolling resistance. Page 1 of 1 x close Low-roll ing-resistance tires, like those on the Toyota Prius, are a key component in the overall system that makes hybrid vehicles so fuel efficient. Consumer Reporfs is the only organization that regularly publishes a rolling resistance score as part of its ratings of important tire-performance criteria. We note rolling resistance for all the tires we test except winter tires, where traction and grip are of paramount importance. While proper inflation pressure is the first step toward optimum fuel economy and long tire life, rolling resistance can add or detract an additional one or two miles per gallon. Therefore, smart tire selection is among the most cost- effective means of optimizing your vehicle's fuel economy because you generally don't have to pay more to get a tire with better rolling resistance. The reward for replacing a worn, less-optimum tire could be more than $100 in annual fuel savings. GET THE MOST FROM YOUR TIRES • Keep your tires properly inflated. (A label on the driver's doorjamb tells you the correct pressures to use.) • Check inflation pressure at least monthly, when the tires are cool. • If you were happy with the tires that came with the car when it was new, consider replacing them with an identical set. Low rolling resistance is a common trait oforiginal-equipment tires. • Before buying replacement tires, check Consumer Reports' P.atings for tires that excel both in low rolling resistance and overall performance. http://www.consumerreports.org/cro/cars/tires-auto-parts/tires/low-rolling-resistance-tires-... 1 /13/2009